As such a clamping apparatus, conventionally, there is a clamping apparatus described in the Patent Document 1 (Japanese Unexamined Patent Publication No. 2001-38564). This conventional art is structured as follows.
A piston is vertically movably inserted into a housing of a reference block; a spring chamber for locking is formed above the piston; and in the spring chamber, a large number of coned disc springs vertically superposed on one another are attached. Further, below the piston, a release chamber where pressurized oil is supplied and discharged is formed. An annular plug portion is projected upward from the housing. Between an outer peripheral surface of the annular plug portion and a tapered hole of a movable block, a diametrically expandable and contractible tapered sleeve is interposed. A coned disc spring which urges the sleeve upward with a predetermined force is attached between an under surface of the sleeve and an outer surface of the housing. An output rod is vertically movably inserted into a cylindrical hole of the plug portion, and the output rod is connected to the piston.